This invention relates to a method and an apparatus for monitoring a variable in a system.
Prior art methods of this type include, periodically or continuously, sensing a value of the variable, and comparing the sensed value, with a constant threshold. If the sensed value falls below the threshold, the quality of the variable, and hence of the system is indicated as no longer satisfactory.
Examples where methods of this type are useful are monitoring insulation between two-walled pipelines, or checking of cable shafts for moisture. The threshold below which unsatisfactory quality is indicated is generally a function of a certain intent, requirement, rule, or predetermined value.
In a known system of this type, the threshold is permanently set for each monitoring task in stepping switches or potentiometers, either at a factory, or manually during use at the discretion of a user. The threshold is determined in each case from an understanding of a required quality of the system in dependence upon the type of sensor used to measure the variable.
In certain circumstances there exists a discretionary margin or a difference of opinion regarding the threshold. For example, a person responsible for the quality may think the threshold is too high, while another person who could possibly be harmed, may think the threshold is too low. Thus it is possible that identical circumstances could result in a complaint from one user that a report of unsatisfactory quality comes too late while another user complains that the report comes too early.